R.Novotny a* , S. F. Burachas d , W. Döring a , V. Dormenev b ,

R.Novotnya*, S. F. Burachasd, W. Döringa, V. Dormenevb, Y. M. Goncharenkoc, M. S. Ippolitovd, A. Hofstaettere, M. Korzhikb,

V. Mankod, Y. M. Melnickd, O. Missevitchb,V. V. Mochalovc, V. Ryazantsevc, P. A. Semenovc, G. Tamulaitisf, A. V. Uzunianc,

A. Vasilievd, A. N. Vasilievc and for the PANDA collaboration

aII. Physics Institute, University Giessen, Heinrich-Buff-Ring 16, 35392 Giessen, Germany

bINP, Belarus State University, 11 Bobruiskaya, 220030 Minsk, Belarusc Institute for High Energy Physics, Protvino, Russia

dR.RC Kurchatov Institute, Moscow, RussiaeI. Physics Institute, University Giessen, Heinrich-Buff-Ring 16, 35392 Giessen, Germany

fVilnius University, Vilnius, Lithuania

Radiation hardness and recovery processes of PWO crystals

at –25oC

SCINT 07 R.Novotny 1SCINT 07 R.Novotny 1

• high resolution calorimetry with PWO CMS – HYCAL – DVCS – ALICE - PANDA• the experimental facility at IHEP• experimental results• interpretation

decay kinetics – defects - impurities• consequences, further experiments and outlook

SCINT 07 R.Novotny 2


• high resolution calorimetry with PWO

+ fast and very dense scintillator: <10ns Xo=0.9cm

+ radiation hard @RT: CMS-ECAL

- low light yield: medium-energy application

improvement of the photon statistics by:• increase of light output PWO-II• operation well below room temperature

0 200 400 600 800 10000

20

40

60

80

100

LY

/ p

.e./M

eV

integration gate / ns

-25oC

-10oC

-0oC+10oC+25oC

photon energy / MeV

/ E

%

excellent energy resolutionachievable at low temperatures

envisaged operation at T = -25oC

PHOS (PHOton Spectrometer) 17920 PWO channels (22x22x180mm3)

study of initial phase of HI collision: via direct photons, high pT ,

PHOS @ALICE LHC EMC @PANDA - FAIR

20000 PWO channels (20x20x200mm3)

hadron physics with anti-protons


no permanent damage due to defect formation activation due to proton induced reactions reduction of optical transmission

can be handled by monitoring

dose:1013 protonsEp = 90 MeV@ KVI, Groningen

wavelength / nm

tran

smis

sion

/ %

both experiments can expect a lower radiation dose


all tests of radiation hardness have been so far performed at RT

• the experimental facility at IHEP Protvino

schematic layout



cooling machine

-source

crystal container

coolingmachine

crystal container


Bq105dt

dN 12

137Cs-

source

dose rateprofile /a.u.

air PWO

the samples to be tested

irradiation time / h

rela

t. P

M-c

urr

ent

dose rate 20rad/h

LY(-20oC)/LY(+20oC)

sam

ple

s


the typical behavior

• @RT small tranmission loss fast saturation• @ T=-23oC increase of light yield no saturation due to

slow recovery

similar behavior at lowerdose rate of 2rad/h (upper limit @PANDA)


recovery after irradiation

time / h

tran

smit

tan

ce @

455n

m /

a.u

.

at low temperatures no improvement of the transmittance with time


irradiation of PWO-II crystalslig

ht

yiel

d /

pe/

MeV

integration gate / ns

-25oC

0oC

+25oC

time / h

PM

T o

utp

ut

/ a.u

.

2 rad/h 20 rad/h

+20 C -25 C

PWO-II - 28

PWO-II - 30


recovery process at +20C

recovery process at -25C

time / h

PM

T o

utp

ut

/ a.u

irradiation of PWO-II crystals


Crystal ID

LY* @ RT [p.e./MeV]

ratio, DC@-25C/ DC@+20C

signal loss (%) after 310 h of irradiation

@ 2 rad/h &-25C

DC Blue LED Red LED

3 19.1 3.4 50 19 9

27 19.5 3.4 20 7 1

28 19.6 3.4 19 5 1

29 17.8 3.4 36 13 6

30 19.8 3.5 32 10 3

37 21.1 3.3 29 8 3

* LY – light yield measured by RINC, Minsk



crystal #94 (large)

crystal #136 (small)

irradiation of PWO crystals of CMS-type:different concentration of dopants

dose rate 2rad/h @ -25oC

scintillation signal

time / h

rela

tive

PM

res

pon

se

blue LED signal


interpretations and (?) solutions

wavelength / nm

tran

smit

tan

ce /

%

@RT

R.-Y. Zhu et al, IEEE Trans. on Nucl. Scí. (2004)

ind

uced

abs

orpt

ion

/ m

-1

irradiation time / min

M.Korzhik et al.


time / s

k /

k0

long release times: V.Dormenev, M.Korzhik et al.

• analysis of TSL data up to 230K delivers no slow time constantsat –10oC or –25oC

• center @580meV (observed in pure PWO) should be suppressed by La/Y doping

• deep trap @700meV (Frenkel defect)

• induced absorption @400nm• release time ~ 2.8h @RT• release time = 125h @ -10oC

= 808h @ -25oC

operation of the calorimeter at –10oC not sufficient



origin of slow recovery processes S. Burachas et al.

results are related to radiation induced structural changes in inclusions of variable valency tungstate oxide complexes WO3-x

due to re-arrangement of oxygen ions.

S.Burachas et al., J. Crystal Growth 293(2006)62

the changes proceed slower at reduced temperatures

thermal energy insufficient for recovery

recovery after fast neutron irradiation

1,2: b/a red.annealing1´,2´: b/a n-irradiation

induced absorption of PWO after irradiation: 20krad (60Co) @ RT

350 400 450 500 5500,0

0,2

0,4

0,6

0,8

1,0

Lumi

nesce

nce i

ntens

ity (no

rmaliz

ed)

Wavelength (nm)

Excitation 325 nmT

Meas 250 K

exc.@325nmT=250K

• Mo as a contributor to the optical absorption induced in PWO (A.Hofstaetter et al.)


Hofstaetter, R. Oeder, A. Scharmann, et al.phys. stat. sol. (b) 89, 375 (1978)

thermoluminescence of PbWO4/PbMoO4 mixed crystals


crystals were irradiated with 50keV x-rays

temperature of maximum thermal decaydepends strongly on the Mo-content.

34Mo

responsible trap: MoO4 tetrahedron

identification via EPR


ESR measurements identify the complex in PWO-II crystals


optical absorption due to (MoO4)3- ?

difference in optical absorption of CaWO4:Pb: • irradiation with x-rays @T = 77 K• subsequent annealing

M. Böhm, R. Grasser et al.,J. de Physique C6, 508 (1980)


is it relevant for PWO-II crystals?


energy / eV

opti

cal a

bso

rpti

on

Emax=2.35eVFWHM=0.8eV

wavelength / nm

PbW(1-x)O4/PbMoxO4, x=0.001

0

20

40

60

80

100

120

140

180 200 220 240 260 280 300

Temperature, K

TL

, a.u

.

Experimental data

Sum of the 3 peaks

1st peak

2nd peak

3rd peak


in contrast: evaluations of the TSL-parameters in the temperaturerange between 180K and 300K by Korzhik et al. lead

to trap-lifetimes of 4 < < 250s @ 248K

• consequences, further experiments and outlook 1/3

• optimum experimental resolution and stabilization (constant term)will rely on very sophisticated monitoring

probably not!

• online bleaching


bleaching wavelength / nm

ES

R in

ten

sity

/ a.

u.


• more conclusive investigations

irradiation of PWO crystal @ -25oC with1.2MeV photons (60Co) @GI

andmeasurement of optical transmission

of the cooled crystal @ -25oC

• modification of doping or further reduction of impurities (Mo?)



• operation at higher temperature: test performed at T= 0oC !

central detector3x3 matrix

ring of neighbors E=40.9MeV

/E = 9.5%

energy / a.u.

cou

nts

3x3 matrix of PWO-II crystals20x20x200mm3

readout with LAAPDs

0 , 0

1 , 0

2 , 0

3 , 0

4 , 0

5 , 0

6 , 0

7 , 0

8 , 0

9 , 0

1 0 , 0

0 , 0 0 , 1 0 , 2 0 , 3 0 , 4 0 , 5 0 , 6 0 , 7

p h o t o n e n e r g y / G e V

/ E = 2 . 4 6 % @ E = 1 G e V

14.2)GeV/Eln(22.2GeV/E

21.1

E

p h o t o n e n e r g y / G e V

/ E

[%

]


+20○C

-25○C

2 rad/h 20 rad/hPMT anode signals under different modes of crystal irradiation by 137Cs gamma-source


Recovery process at +20C

Recovery process at -25C


VB

CB

0

-0.25

-0.5

-0.75

-1

eV

-4.1

(WO4)3-

(WO4)3- -SE3+

(MoO4)3-

Pb+ -VO

325 nm

Documents

R.Novotny a* , S. F. Burachas d , W. Döring a , V. Dormenev b ,